In the assembly of a hard disk, a step for fixing portions around a magnetic head using a bonding agent is indispensable, and, for example, there are steps, such as fixing a piezoelectric device, fixing a magnetic head, and fixing a magnetic head to a suspension {head gimbal assembly (HGA)}. With respect to the bonding agent used in these steps, for example, patent document 1 discloses a photocurable composition comprising a radically polymerizable monomer (which produces a polymer having a glass transition temperature of 25° C. or higher), such as (a)an (meth)acrylate compound, and patent document 2 discloses a thermosetting epoxy bonding agent having a glass transition temperature higher than 85° C.